Method of producing iron and alloys of iron having a very low percentage of carbon



Patented Nov. 13, 1928.

I UNITED STATES PATENT OFFICE,

HENNING GUSTAV FLODIN, BOSLAGS-NASBY, AND EMIL GUST TOBVAL'D GUS- IAIBSON, OF STOCKHOLM, SWEDEN, ASSIGNOBS T0 HAMPUS GUSTAF EMRIK COR- NELIUS, OF STOGKEOLM, SWEDEN.

mnrnon or raonucms mon Ann'aLLoYs or mom HAVING A vEnY LOW rnncmrr- AGE or cannon.

No Drawing. Application filed June 22; 1925; serial No. 38,940, and in Sweden Kay 11, 1925.

In the methods heretofore used. for producing iron and other carbon-binding metals and alloys thereof it has been found very difficult to produce continuously such metals in a molten state with a very low percentage of carbon, for instance not exceeding 0.05%. According to various methods, single charges have attained such a low percentage of carbon, it is true, but with such an uncertainty that production according to these methods on a larger scale has not been possible. As far as we are aware, percentages of carbon of 0.03 and less have been attained in commercial operation only in'very rarely Q tically continuously and reduced and occurring exceptional cases. Therefore, iron and other carbon-binding metals with such a low percentage of carbon have commanded excessive prices as compared with I metals holding, for instance, 0.10% of carbon.

' According to the method worked out by us for producing, carbon-binding metals and alloys thereof, which are low in, carbon, directly out of oxide ores, for example, in conformity to our patent application Serial No. 756,557, the ore is finely crushed and intimately mixed'with finely divided carbon or carbonaceous material and, in some cases with some other reducing agent, the mixture being then, if desired. with the use of a suitable binding agent and in connection with a drying process transformed into briquettes or pieces with the particles of the reducing agent and the grains-of ore fixed-v as regards their mutual positions, and the briquettes or pieces being fed into an electric 1 fiurnace preferably continuously or pra'c melted in said furnace in a non-oxidizing atmos- 40' phere at the surface of a slag-bath formed during reduction or especially prepared before the-feeding in of the charge, e. the briquettes are reduced and melted whilst lying or floating on top of the slag bath.

By this method we have been successful in producing continuously, on a commercial scale, ingot metal both in the form of iron and as alloyed iron with percentages of carbon varying between 0.05 and 0.10%. At

the same time, the percentage of metal ox- ,ides in the slag formed has been kept within very low or reasonable limits, so that the lossof metal in the slag hasbeen very small or immaterial. The amount of reducing agent added in the form of carbon or carbonaceous material, if desired, together with other reducing agents, such as ferro-silicon, ferro-mangancse, ferro-silicon, aluminrum, ferro aluminium silicon or the like, has been so adapted that the quantity of active reducing agent in the briquettes or the pieces corresponds to the quantity required for the amount of ore involved and for the carbonization of the metal formed.

We. have found, however, that by proportioning the quantity of 'the reducing agent added, the main portion of which is always constituted by carbon-or carbonaceous material i. e. the process isalways endothermic, so that there is a shortness of active reducing agent in the briquettes or pieces with res ect to the quantity required for the amount 0 ore involved, still lower percentages of carbon willbe'attained in the metal formed. The use of this shortness of reducin agent forms the characteristic features of ts e present in:

vention. When carbon only is used as a re- .ducing agent, we have found,'-'for instance,

with a shortness in the briquettes or pieces of at least 5% of active carbon, the operation in the electric furnace being otherwise suitably adapted, that a metalwill be obtained having a percentage of carbon not exceedmg 0.03%, which result is attained in continuous operation, i. e. one charge after an:

"other. Obviously,.the loss of metal in theflag will be greater when using such a shortness of reducing agent, but this loss is perfectly compensated by the greater value of the metal obtained owing to its low percentage in carbon.

In this connection, the expression active reducing agent, that is to say, carbon alone or admixed with some other reducing a cut, meansthe reducing agent that is avai able for the-reduction of the metal oxides in the briquettes or pieces, after the quantities required for other purposes have been deducted. Thus, if the briquettes or pieces contain, for example, carbonic acid or water, which,'when feeding is effected into the fur nace, are permitted to react with the reducing agent involved, a quantity of the reducing agent equivalent to the carbonic'acid and the water will be consumed, and cannot be regarded as active for the reduction of the y gen contained in thecarbonaceous material,

- electrodes that can be raised and lowered. 3 Among other things, the slag will-be more may in the same way entail a non-desirable but unavoidable consumption of carbon.

By reason of a shortness of carbon being present in the briquettes or pieces, i. e. the

quantity of active carbon not coming up to the quantity required for the reduction of the metal oxide, which shortness is evenly distributed in the same, the metal drops formed during the reduction in the slag bath have no occasion appreciably to combine with carbon. A metal which is very poor in carbon will thus accumulate at the bottom of the furnace below the slag which is rich in metal oxides, such slag may have, in turn, to a certain degree a refining action on the metal, which action is the more powerful the higher the percentage is of metal oxides, for instance, of ferrous oxide, in the slag.

Irrespective of this refining action of the.

slag the result is that a metal very low in carbon is obtained on tapping, provided the operation of the furnace is otherwise properl conducted..

en reducing and melting bri uettes short of active reducing agent, in the e ectric furnace, the slag will, as already set forth contain a rather considerable quantity of metal oxides, and Will then, as a rule, be more quick-flowing than a slag containing less metal oxides, the composition otherwise remaining the same. When operating with carbon electrodes in the furnace, whichmethod appears to be the most common,-this circumstance is of a decided disadvantage for the reducing process proper, when carrying out the process in an electric furnace having one or more downwardly extending conductivethan before, whereby the resistance of the slag and thus the development of heat in the slag bath proper will..be less when the furnace is run with the electrodes close to or sunk into the slag. The length of the electric arcs will also be greater, and, consequently, the temperature in the upper portion of the furnace will rise, whereas by the reduced temperature of the slag the metal formed at the bottom of the furnace will be relatively cold. By the quick-flowing properties of the slag, the latter is apt to splash up onto the electrodes when the charge is "fed into the furnace, and metal rather rich in carbon will thus be reduced out oifihe slag by the electrode carbon thereby incfliising the percentage of carbon of the metal produced. By reason of the high percentage of metal oxides in the slag the furnace should be run with the electrodes as far as possible out of contact with the slag bath in the electric furnace when a charge is used which is low in carbon.

In order to obviate this drawback, the slag is made viscous preferably by adding into the furnace substances having the property of rendering the slag viscous, such substances being, for instance, lime, dolomite, quartz, sand or the like, such addition being effected in admixturewith the charge or direct into the furnace or in both these manners. The kind of substance selected and the quantity thereof used must evidently be adapted to the substances contained in the'gangue and in any of the binding agents and admixtures. For example, if a basic slag is formed in melting the charge, lime or. dolomite should be added. If, on the other. hand, an acid slag is formed, quartz or sand is preferably added.

By the addition of such substances, for instance, to the sla in the furnace, the conductivity of the s ag will also be reduced. It will then be possible, prior to tapping, to increase the temperature of the metal reduced by operating the-furnace with the.

the electric furnace, either mixed together or in any sequence after each other. If different kmds of charges are used for the various ores, the percentages of active reducing agent 1n the variousv charges are proportioned so that therewill be a shortness of reducing agentin the total quantity'of the char es. he amount of. reducing a ent in the ifierent char 1 ma .then, pre erably,

be so proportion that t ere is a shortness in the charge of the-more readily reduced metal, whereas in the charge of metal which is more difiicult to .reduce, the quantity-of active reducing agent corresponds to; the amount which is theoretically required. In some cases it may be more suitable to have a shortness of reducing agent in the metal which is more difiicult to reduce. The invention does not, however, depend on which kind or kinds of charges are short of reducing agent, only that a shortness of said nature existsin the total'amount of char e.

For utilizingany. metals contained int c slag in the form of metal oxides, it is preferable, prior to tappingEtc add a thermic re.-

ferro-alumin'ium, silicon, al um or the like, to the slag in the furnace. For this purpose ferro-silicon will be found particularly suitable by reason of its cheapness. Obviously, the reducin agent added to the slag should be as free rom carbon as possible, and when added it is preferably distributed over aslarge aportlon ofthe slag bath as possible. The metal or alloy added, having a great allinity for oxygen, will then reduce out of the slag quantities of iron, chromium or other metal contained in the slag, equivalent to its oxygen-absorbing capacity. The metals thus. reduced sink down through the. slag into the metal already reduced. At the same time the smaller percentage of metal oxides decreases the electrical conductivity of the slag, so

'that prior to tapping the furnace may be operated with the electrodes immersed into the slag and run with resistance, thereby increasing the temperature of the molten metal. If a suitable quantity of lime, dolomite, or the like for bindingthe silicic acid, alumina etc. formed is added simultaneously with or immediately after the ferro-silicon, the electrical resistance of the slag will be further increased, besides which a slag will be obtained which is more suited to the lining of the furnace.

It will be advanta eous to charge with briquettes composed or an intimate mixture of the thermic reducing agent and the substance added for binding the by-products formed in the reaction of the thermic re ducing agent with the metal oxides in the slag. The lime, dolomite or the like will then more readily act on the silicic acid formed.

The molten metal obtained may be deoxidized during or after the tapping, in known manner by the addition of ferromanganese and, if desired, of ferro-silicon to increase the densit of the metal, but in this case admixtures s ould be used Which are low in carbon, in order that an increase of the percentage of carbon of the metal shall not take place.

As illustrative examples ofthe process according to the invention the following may be used. V

For the production of iron having a carbon content not exceeding .05% according to the present invention we may proceed as follows:

Finely divided iron oxide ore and finely divided carbon in the form of, for instance, charcoal, coke or anthracite as well as a suitable binding agent are thoroughly mixed in such a proportion that the quantity of active carbon in the mixture amounts to 90 to 95% of the quantity theoretically required for the complete reduction of the ore. If carbonaceous binding agent is used, the percentage of active carbon in said agent must also be paid regard to in calculating the quantity of reducing agent. However, the binding agent should preferably consist of lime water pre pared by slaking burnt lime, as lime must always be used in the process in order to obtain a suitable slag having a suflicient high resistance to give the underlying metal the necessary high temperature. However, to the mixture only such quantity of lime water is supplied as is required to bind the grains of the ore and the carbon particles to each other, whereas the remaining quantity of the lime necessary for a good working is preferably added directly to the furnace during the course of the smelting. Then the mixture thus obtained is transformed into briquettes which are then dried, until the water is removed and the grains of the ore and the carbon particles are fixed intheir mutual positions by the binding agent which is transformed into solid state.

The briquettes are then fed into the electric furnace, preferably continuously or in small portions at intervals adapted to a regular course of the reduction. The briquettes.

are reduced and melted lying in a thin layer at the surface of the slag bath in the furnace. In the reduction of the ore small iron drops very low in carbon are found which sink down through the slag and collect at the bottom of the furnace. When a suflicient quantit-y of iron is formed, the iron is in known manner tapped to a ladle to be cast in moulds. before tapping in the moulds by adding ferro-manganese to the furnace or to the iron in the ladle, but as a rule no deoxidation is re quired. Before tapping a test is taken of the iron for ascertaining its temperature. If the temperature is not sufliciently high for obtaining the necessary temperature of the iron in the moulds, the iron is heated before tapping by running the furnace during an adequate length of time with the electrodes immersed in the slag.

F or the production of so called rustless iron having a percentage of chromium of about 13% we-may proceed as follows:

Briquettes are prepared in the manner set forth above of finely divided iron ore, finely divided chromium ore, finely divided carbonaceous material and a suitable binding agent. stituents in the briquettes may be 60 parts by weight of iron containing 63% Fe in the form of Fe O 40 parts by weight of chromium ore having 51.6% Cr O and 13.8% Fee.

16, parts by weight of charcoal containing 77% C, and

10 parts by weight of burnt lime.

By successively introducing and melting said briquettes in the electric furnace a metal bath is obtained containigg about 10% Cr and about .07 C and a reat quantity of slag rich in Cr O and F e0, Then per 100 The proportions of the dilferent con-' If desired, the iron is deoxidized after the addition of ferro-silicon a suitable kg. of ore 3 to 5 kg. of ferro-silicon containing Si is introduced directly onto the slag or a correspondingly smaller quantit ofa ferro-silicon richer in Si. By the addltion of ferro-silicon the greatest part of the content of Cr O and FeO in the slag is reduced, the chromium and iron thus produced sinking down into the metal bath and joining with same. The metal bath thus obtamed contains about 13 to 15% of'chromium and about .07 to 12% carbon, the some- What increased content of carbon depending on the carbon'content in the ferro-silicon used. T he content of Si in the metal is about .10 to 20%. Simultaneously with or quantity of lime may be added to the slag to bind the silica formed in the reaction of ferro-sil con with the metal oxides in the slag. On account of the decreased contentin the slag of metal oxides, the electric conductivityiof the slag will be decreased which is of advantage, as the temperature of the slag will thereby 'be increased and, conse.

upon ferro-silicon is added to the newslag formed. The reason of proceeding in this manner is that on account of the great percentage of gangue in the chromium ore a great quantity of slag will be formed making such a tapping of slag suitable, it being difiicult to run the furnace with so great quantity of slag as would be present in the furnace, if an intermediate tapping of slag is not made.

The invention is not limited to the metals I or metal alloys or the admixtures etc. which have been mentioned hereinbefore by way of example only, but comprises any manufacture of metals very low in carbon and possessing carbon-binding properties, or any alloy of such metal, by the method herein set forth, in which a shortness of active carbon and if desired of other reducing agents, is used. c

What we claim as new and desire to secure by Letters Patent of the United States of America is 1. In a reduction processfor producin iron and other carbon binding metal an alloys thereof low in carbon directly from oxide ore in an electric furnace in a nonoxidizing atmosphere, the step of charging vided carbonaceous reducin .material, the

uantity of reducing agent eing less than t e theoretical amountrequired for reduction' of the ore.

2. In a reduction process for producing iron and other carbon binding metal and alloys thereof low in carbon directly from oxide ore in an electric furnace in a nonoxidizing atmosphere, the step of charging said furnace with briquettes of intimately mixed finely divided oxide ore and finely d1- vided reducing material including carbonaceous material, the uantity of reducing agent being less than t e theoretical amount required for reduction of the ore.

3. In a reduction process for producin iron and other carbon binding metal and a loys thereof low in carbon directly from ox ide ore in an electric furnace in a non-oxidizing atmosphere, the steps of charging onte-a slag bath in the furnace briquettes of intimately mixed finely divided oxide ore and finely divided reducing material including carbonaceous material, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore, and melting the briquettes at the surface of said slag bath.

4. In a reduction process for producing iron and other carbon binding metal and a loys thereof low in carbon directly from oxide ore in an electric furnace in a nonoxidizin atmosphere, the steps of charging practicafiy continuously onto a sla bath in the furnace briquettes of intimately mixed finely. divided oxide ore and finely divided carbonaceous reducing material, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore, and successively melting the briquettes at the surface of said slag bath.

5. In a reduction process for producing low-carbon alloys of iron and other carbon binding metal directly from oxide ores in .an electric furnace in a non-oxidlzing atmosphere, the steps of charging said furnace with briquettes; of intimately mixed finely.

divided oxide'ore of the base metal of the alloy to be produced and finely divided carbonaceous material as reducing agent, and with briquettes of intimately mixed finely divided oxide ore of the alloy constituent andfinely divided reducing material including carbonaceous material as reducing agent,

the total quantity of reducing agent in both.

kinds of briquettes bein less than the theoretical amount required for reduction of the ores.

6. In a reduction process forproducing iron and other carbon binding metal and alloys thereof low in carbon directly from oxide ore in an electric furnace in a non-oxidizing atmosphere, the steps of charging said furnace with briquettes of intimately mixed finely divided oxide ore and finely divided the ore, and meltin making viscous the s ag forme during said melting.

7. In aired uction process for producing iron and other carbon bindin metals and alloys thereof low'in' carbon irectly from oxide ore in an electric furnace in a nonox-idizing' atmosphere, charging said furnace with briquettes of intimately mixed finely divided oxide ore and finely divided carbonaceous reducing material, 'the quanity of reducing agent bein lessthan the theoretical amount re uired For reduction of the ore, melting the ri uettes and adding during said melting a su stance to increase the viscosity of the formed slag 8. In a reduction process fo'rproducing iron having a ercentage of carbon not'exceeding .05% irectly from iron oxide ore in an electric furnace in a non-oxidizing atmosphere, the step of chargin said furnace with briquettes of intimaely mixed finely divided iron oxide ore and finely divided carbonaceous reducing material, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore.

9. An endothermic reduction process for producing iron and other carbon binding metals and alloys thereof low in carbon directly from oxide ore, consisting in reducing and meltingin an electric furnace in a non-oxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidified, the quantity of reducing agent being less than. the theoretical amount required for reduction of the ore, and decreasing during melting the electric conductivity of the slag formed.

10. An endothermic reduction process for producing iron and other carbon binding metals and alloys thereof'low in carbon directly from oxide ore, consisting in reducing and melting in an electric furnace in a nonoxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidfied, the quantity of reducing agent being less than the theoretical amount r uired for reduction of the ore, decreasing uring meltin the electric conductivity of the slag forme and running the furnace, immediately prior to tapping, for an adequate length of time withthe electrode immersed in the slag J" 11. An endothermic reduction process for producing iron and other carbon binding metals and alloys thereof low in carbon directly from oxide ore consisting in reducing and melting 1n an electric furnace ma nonoxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidified, the quantity of reduc'ng agent being less than the theoretical amount required for reduction of the ore, and decreasing the electric conductivity of the slag formed and. liberating metal of the metal oxides in the slag by'ad'ding a thermic reducing agent to the slag bath.

12 An endothermic reduction process for producing iron and other carbon binding metals and allo 5 thereof low in carbon directly from oxi e ore, consisting in reducing and melting in an electric furnace in a nonoxidizing atmosphere a, charge composed of finely divided oxide ore and finely divided carbonaceous reducing material,.mixed and solidified, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore, and decreasing the electric conductivity of the slag formed and liberating metal of the metal oxides in the slag by adding ferro-silicon to the slag bath.

13. An endothermic reduction process for producing iron and other carbon binding metals and alloys thereof low in carbon directly from oxide ore, consisting in reducing and melting in an electric furnace in a nonoxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidified, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore, and decreasing the electric conductivity of the slag formed and liberating metal of the metal oxides in the slag by adding' to the slag bath a thermic reducing agent and a substance capable of binding the by-products -formed in the reaction of the thermic reducing agent with the metal oxides in the slag.

14. An endothermic reduction process for producing iron and other carbon binding metals and. alloys thereof low in carbon directly from oxide ore, consisting in reducing and melting in an electric furnace in a nonoxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidified, the quantity of reducing agent being less than the theoretical. amount reuired for reduction of the ore, decreasing t e electric conductivit of tleslag formed and liberatin metal 0 the metal oxides in the slag by a ding to the slag bath a thermic reducing agent and a substance capable of' rectly from oxide ore consisting in reducing and melting in an electric furnace in a non-oxidizing atmosphere a charge composed of finely divided oxide ore and finely divided carbonaceous reducing material, mixed and solidified, the quantity of reducing agent being less than the theoretical amount required for reduction of the ore,

and decreasing the electric conductivity of the slag formed and liberating metal of the metal oxides in the slag by adding to the slag briquettes composed of a thermic reducing agent and a substance capable of binding the by-products formed in the reaction of the thermic reducing agent with the metal oxides in the sla 16. In a reducion process for producing rustless iron and steel directly from oxide ores in an electric furnace in a non-oxidizing atmosphere, the steps of charging onto a slag bath in the furnace briquettes of intimately mixed finely divided chromium oxide ore and iron oxide ore and finely divided carbonaceous reducing material, the quantity ofreducing agent being less than the theorectical amount required for reduction of the ores, melting the briquettes at the surface of the slag bath, and decreasing the electric conductivlty of the slag formed and liberating metal of the metal oxides in the slag by adding ferro-silic'on to the slag bath.

In testimony whereof we afiix our signatures.

usnumc GUSTAV FLODIN.

EMIL cusTAr TORVALD cusnrsson. 

